It is known to bring about colored structures, e.g. inscriptions on a glass, by applying a paste containing metallic salts to the glass surface by mask, screen or dabber printing in the desired structure via a subsequent heat treatment. Metallic ions were incorporated into the glass layer adjacent to the surface (by doping) before; they are reduced to atoms, which coalesce to form metallic particles (coagulation), by reducing agents contained in the glass and under the influence of a temperature. DE 40 13 300 discloses a practical application of this method to apply an inscription to a windscreen for automobiles in which a filter strip which attenuates light and heat irradiation is imprinted by means of the screen printing technique. The known method uses this technology in coloring glasses in which additives in the form of metallic salts are admixed to a glass melt. During a subsequent annealing, via ion exchange processes near the glass surface, reducing agents in the glass help cause the formation of atoms, which coalesce into metallic particles, thus bringing about a coloration. Gold, copper, and silver salts or their atoms are particularly suited for coloring the glass in the visible spectral range. Disadvantages of the known inscription method are the relative high labor consumption because of a plurality of production steps and the need to manufacture appropriate masks for each structure desired. Moreover, the colored structures which can be produced in this manner are confined, in their minimum possible size and also pin precision, by the masks and the diffusion process so that this way makes it impossible to produce colored structures having dimensions in the μm range.
It is further known to use laser beams for producing colored structures and engravings having dimensions up to the μm range on surfaces of glass, plastics, metals, ceramics, etc. These methods rely on a local destruction of the surface structure by material erosion, evaporation, melting or burning in foreign material. Local destructions of the surface structure result in a decrease in the mechanical stressability of glass that cannot be accepted for many applications. Moreover, the structures are directly on the surface of the glass and, hence, can be easily attacked both mechanically and chemically.
U.S. Pat. No. 4,769,310 has made known a method for the production of markings in ceramics or glasses that contain inorganic compounds sensitive to irradiation. The markings produced by this method are also located in layers adjacent to the surface.
U.S. Pat. No. 5,206,496 discloses a method for the production of structures which not only are flat-spread, but also spatial, in the volumes of randomly shaped transparent bodies. A focussed beam of a high energy density, for which the material is transparent, is directed onto a body made of glass or plastic. In the focus which is in the interior of the body, because of the non-linear optical properties which become efficient only at very high energy densities, the beam causes an ionization of the material and, ultimately, locally confined damage to the material without appreciably modifying the areas outside the focus and the surface of the body. Such damage leads to an extinction in the processed areas which is more intense as compared to the processing material. The increased extinction is provoked by microfissures which scatter incident light, thus making visible the location at which the focus has been. This is a way to produce predetermined structures by a relative movement between the body and focus.
DE 198 41 547 has made it known to produce a variety of colored structures having one, two or three dimensions in the interior of glasses without impairing the mechanical properties of the glass. This is achieved by the fact that such particles are precipitated in small volume elements at any point in the glass which contains ions of metals which color the glass in the form of submicroscopic particles, and the desired color structure is built up by lining up volume elements colored in this way. A locally limited heating of the volume elements can limit the formation of particles to these. Therefore, the known method relies on the production of markings, structures or inscriptions on glasses by means of a laser beam. However, this presupposes that the glasses were been doped before, i.e. contain ions of metals. As mentioned initially this can be achieved by admixing appropriate additives to the molten glass or a paste containing metallic salts is applied to the glass, whereupon a subsequent annealing causes metallic ions to migrate into a layer adjacent to the boundary layer via ion exchange processes and diffusion.
DD 215 776 A1 has made known a method for the manufacture of colored images on glass. The method heats diffusion ink by laser beams simultaneously with the glass surface in accordance with the contours envisaged for the image. On the heated glass surface, the diffusion ink gets into the glass by convection and diffusion, which produces a durable acid-proof and caustic-proof ink track. The disadvantage of this known method is that the glass surface is caused to melt and, thus, its mechanical stability is impaired.